The present invention relates to rotors for turbomachines, such as steam turbines and the like. More specifically, the present invention relates to an apparatus for reducing the power loss associated with windage in the vicinity of the rotor coupling of a turbomachine.
Turbomachines, such as steam and gas turbines and the like, employ a rotor that transmits rotational power to the corresponding rotor of a driven device, which may be an electric generator, compressor, etc. This rotational power is transmitted between the two rotors by a coupling formed by joining together flanges formed at the end of each rotor. The coupling flanges are held together by bolts that extend through holes in the flanges. Nuts are threaded onto each of the ends of the bolts so that the nuts are circumferentially arrayed around the faces of the flanges. Unfortunately, due to the high rotational speed of the rotor, the wind resistance of the array of exposed nuts creates a power loss that degrades the efficiency of the turbomachine.
Traditionally, a close fitting coupling guard has been employed to enclose the coupling and reduce the windage associated with the rotation of the nuts. However, there is still sufficient wind resistance between the nuts and the air within the coupling guard to create a power loss. Consequently, in the past, in a further attempt to reduce windage, a circumferential slot has been machined into the outward face of each coupling flange so that the nuts are enclosed by the slot. A cover placed over the slot isolates the nuts from the air within the coupling guard. Although this arrangement greatly reduces windage, the costs associated with the machining of the rotor flanges do not make this approach cost effective.
It is therefore desirable to provide an apparatus that can be attached to the rotor coupling of a turbomachine to significantly reduce the windage losses.